The Cell Cycle

1

• Structure, function and growth of prokaryote and
  eukaryote cells
• (ii) Cell growth and Cell cycle
• Interphase
• Mitosis
• Mitotic index
• Control of the cell cycle
• Abnormal Cell division cancer cells

2
Cell Cycle

• When cells reach a certain size they must stop
  growing or divide.
• The cell cycle is the period from the formation
  of a new cell until that cell divides itself
• The length of the cycle depends on the cell but
  is usually 8 20 hours

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The Cell Cycle
4
Interphase

• G1 (First Gap Period)
• Cell grows and increases in mass
• Cell membrane ( wall) are increased
• Number of organelles increase
• Chemical preparation for DNA Synthesis (enzymes,
  deoxyribose sugars, nucleotide bases and
  phosphates synthesised)

5
Interphase

• S phase (synthesis)
• Replication of DNA
• Chromosomes held together by centromere
• In animals centriole pairs duplicate

6
Interphase

• G2 (Second gap phase)
• Cell builds up energy reserves
• Increased protein synthesis

7
Mitosis

• Revision complete the mitosis diagram (note
  this is from standard grade)

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Mitosis

• Compare this to your SG diagram.
• Name the stages
• Interphase
• Prophase
• Metaphase
• Telophase
• Cytokinesis
• What features characterise each stage?

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Mitosis

• Prophase
• Chromosomes condense (coil and fold up) to become
  visible.

10
Mitosis prophase cont

• Cytoskeleton disintegrates
• (its components (microtubules) are used to begin
  spindle formation)
• Spindle formation begins between centrosomes (aka
  Microtubule organising centres MTOCs)
• Nuclear Membrane starts to break up

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Mitosis prophase cont
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Mitosis

• Metaphase
• Spindle continues to grow from centrosomes (which
  are now at the poles)
• Chromosomes line up across the centre of the cell

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Mitosis metaphase cont..

• Chromosomes attach to the spindle fibre by the
  kinetochore in the centromere
• The arrangement of the chromosomes across the
  equator is also known as the metaphase plate.

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Mitosis metaphase cont
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Mitosis

• Anaphase
• Centromeres divide
• Sister chromatids separate and the chromosomes
  are pulled to the poles

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Mitosis anaphase cont
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Mitosis

• Telophase
• Chromosomes begin to de-condense
• Nuclear membrane reforms
• Spindle disassembles and reassembles as the
  cytoskeleton in the 2 new cells

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Mitosis telophase cont
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Cytokinesis

• Dividing of the cytoplasm and organelles
• Animals
• Cytoplasm is pinched by a ring of contractile
  microfilaments (made up of the proteins actin and
  myosin)
• As the ring gets smaller it forms a cleavage
  furrow

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Cytokinesis cont
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Cytokinesis cont

• In plants
• Membrane vesicles spread across the equator of
  the cell.
• They merge to form plasma membrane
• The new membranes lay down the cell wall between
  the two cells.

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Cytokinesis cont
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Mitotic Index

• The fraction (or percentage) in a microscope
  field that contain condensed chromosomes (i.e.
  Undergoing mitosis)

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Learning Activities

• Look at web animations
• www.biozone.co.uk/links.html
• Cell biology Mitosis / Meiosis How cells
  divide
• Posters
• Card sort (pictures / names / descriptions)
• Read Dart pg 9-14 and take notes
• Use Scholar
• Advanced Higher Questions